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Thread: diy 500W smps with voltage or current regulation

  1. #31
    Silvio , can I drive fet directly from SG3525 or need use some of the drivers ?

  2. #32
    diysmps Senior Member Silvio's Avatar
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    No you cannot use it directly for half bridge topology. You need isolation between the high side and low side fet. I think an IR2110 is a good driver to fit after the SG3525 it can source and sink up to 2 amps of current. This will allow you to use even high power mosfets like IRFP460 etc. However for 500 watts IRF740 mosfets are enough.

  3. #33
    Hi
    After few days I'm work on new circuit diagram for my smps with SG3525 and IR2110 , if you can look and say me if you see some mistake ?
    First test is be with 25 kHz on output to FET (50kHz internal oscillator ) and work is on firs look fine , on space for primary transformers coil I m put bulb 60W , all is look fine , but I m see that is not ok because on that power consuming FET is be little hot (maybe 50 celsius degree ) and all so IR2110 is be same temperature .
    Then I m change frequency to 80 kHz on FET (160kHz internal ) and when I m ON smps then is firs blow IR2110 and after that boot FET and SG3525 .
    Have you idea why that is happen , all so GND line from PWM module is burn .



    500W-halfbridge-smps.jpg500W-halfbridge-smps.jpg

  4. #34
    diysmps Senior Member Silvio's Avatar
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    1)Let me see your setup PCB etc
    2) some general rules that you have to take when building smps. Good supply decoupling near the drive chips SG and IR.
    3) Make the drive wires or traces as short as possible to the gates of fets and also away from high current paths
    4) Check SG and IR output driving a couple of LEDs with 12v and 1k series resistors. Check wave form it should be nice and square on both outputs. Check also dead time. (not less than 1uS.
    5) If all is well hook up remaining circuit but leave out the feed back. Hook up bulb instead of trafo and check wave form across bulb. (isolate from grid scope or supply as you will burn scope) You should see a clean square wave. If you have clean wave then proceed with hook up of trafo instead of bulb. Limit current on input with bulb.
    6) Check wave form again and see if any spikes. load smps with 60watt bulb and remove bulb from input. check again for spikes and wave form.

    One last comment a regulated smps should have an output inductor and also minimum load. schematic seems ok in all other things.

    The IR may have burnt after the fet became short circuit and thus burning all SG and ground trace.

    MY advice is to move step by step and check oscillator output and IR output before connection to rest of circuit. YOU MUST START WITH A GOOD WAVEFORM. BEWARE OF FAKE CHIPS
    Last edited by Silvio; 07-31-2017 at 07:18 PM.

  5. #35
    DSC_0011.JPG
    DSC_0015.JPG
    DSC_0010.JPG
    DSC_0019.JPG
    DSC_0018.JPG

    This is few image , like you can see pwm output look nice .

  6. #36
    diysmps Member* res_smps's Avatar
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    try 10K gate to source resistor on each mosfet

  7. #37
    diysmps Member* res_smps's Avatar
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    use ultrafast diode for D2, UF4007 and lowering C16 arround 1 to 10uf
    Last edited by res_smps; 08-01-2017 at 04:56 AM.

  8. #38
    diysmps Senior Member Silvio's Avatar
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    Your setup looks ok and even the wave forms are nice. I was wondering if that wave form is of a loaded psu or off load. The suggestion of a gate source resistor is good from res_smps. This may also go to 1k in value. These will help to shut the mosfets off during the off cycle and not letting any stray inductance switch them on again. However through experience the bootstrap cap may be a bit high but knowing that your operating frequency is 25 Khz their may be enough time for it to charge up.

    All I can say in my SMPS using 3525 and 2110 combination I used 22uF which works well at 60KHz. Be careful but as when at minimum duty cycle if the bootstrap cap is large (45uF) there may not be enough time for it to charge up.

    If you intend to regulate the output you must use an output inductor. I experimented with mine and without it the wave shape at minimum load deforms badly and strange noises of saturation start coming out of the trafo core. However adding it things changed. You have to experiment with the value but with around 30uH is a good start. It must be just enough not to let a high voltage drop at maximum load and stable at minimum load. Headroom must be left in the output voltage to compensate for this though.

    Take also care of your feedback loop that changes in voltage need to have a small delay. A small ceramic cap around 10nF across the TL431 anode and cathode. This will stabilize it.

    It is best to settle first with an unregulated output and see how things behave at full load. You have to adjust the snubber values according to your findings, these tend to differ from a psu to another. The transformer construction need to have good tight coupling with minimum leakage inductance. You can connect the feedback later when you get things stable first.

    One last comment if the output diodes have to handle around 20 amps (24v X 20A= 480 watts) you may need a better heatsink.
    Last edited by Silvio; 08-01-2017 at 08:05 AM.

  9. #39
    diysmps Member* res_smps's Avatar
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    Quote Originally Posted by Silvio View Post

    One last comment if the output diodes have to handle around 20 amps (24v X 20A= 480 watts) you may need a better heatsink.
    dear silvio,

    Please correct me if I am wrong, but I think the diode power dissipation is Vf(diode) x I = 0.7V x 20A = 14 Watt

  10. #40
    diysmps Senior Member Silvio's Avatar
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    Hi I was taking a close look at the component side of the PCB and noticed that you are using the IRFP240 switching mosfets. I took a look at the data sheet and noticed that these fets are only capable of 200 volts. The voltage across these fets is around 320volts. THE VOLTAGE RATING OF THESE FETS IS NOT SUITABLE. Do not be mislead by the fact that only half the voltage is present because its not. It would be a better choice if you use IRFP460 fets instead which are rated at 500v and 20 amps

    As a rule of thumb The current handling of the fets could be calculated as:-

    For continuous rating the drain current of the mosfet divided by 4 (ex. 10 amp mosfet works at 2.5 -3 amps)

    For 50% duty the mosfet drain current handling divided by 3 hence a 10A mosfet works at 3-4 amps

    A brief calculation in your case 155v X 3amps = 465 watts

    A mosfet rated for 10 to 12 amp is suitable. IRF740 will handle the load quite good. if you opt for the irfp 460 well they will be overrated and work very happily. However the IR 2110 can switch both fets with ease.
    Last edited by Silvio; 08-01-2017 at 10:04 AM.

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